U.S. Pat. No. 5,268,439 (W. Hergenrother, T. Bethea, and J. Doshak) disclosed that the use of elastomeric polymers prepared using triorgano substituted-tin lithium initiators in tires resulted in low hysteresis (e.g. low rolling resistance). The triorgano substituted tin of the initiators formed a functional end group on substantially each polymer chain and the tin containing functional group was associated with the lower hysteresis. Tetrahydrofuran (THF), tetramethylethylenediamine and diethylene methyl ether (diglyme) were listed as effective solvents (column 4, lines 26-28). Other polar solvents such as dimethyl ether gave unsatisfactory results (e.g. reaction did not go to completion or the initiator reacts with the solvent column 4, lines 28-33). In column 5, lines 2-27 it is disclosed that a polar coordinator (including tetrahydrofuran and dimethyl ether) may be added to promote randomization in copolymerization and to control vinyl content. The vinyl content of the resulting polymers of the patent examples were from 30 to 49 percent with the higher values being associated with the use of additional polar modifiers, in addition to the tetrahydrofuran associated with the initiator.
U.S. Pat. No. 5,502,129 (W. Hergenrother, W. Smith, A. Muratore, J. Sigle and M. Nemeth) disclosed a two step method of producing the triorgano substituted-tin lithium initiators which reduced the residual chloride content. The reduction in the chloride content was associated with reduced amounts of undesirable volatile organotin compound being released during subsequent processing of polymers produced with the triorgano substituted-tin lithium initiators. This patent generically groups solvents into 1) solvating or solubilizing solvents (which include tetrahydrofuran, glymes, and other ethers) and 2) alkanes. Tetrahydrofuran was the preferred solvating solvent and was used in all the examples. In the process a 3 to 6 fold molar excess of solvating solvent to triorgano tin was desired in the second step but a 0.5-2 fold excess was preferred in the first step to minimize the amount of soluble LiCl carried from the first step into the product.